chore(package): update mocha to version 6.0.1

Closes #33

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
     "yargs": "^12.0.1"
   },
   "devDependencies": {
-    "mocha": "^5.2.0",
+    "mocha": "^6.0.1",
     "nyc": "^12.0.1",
     "shelljs": "^0.8.1",
     "showdown": "^1.8.6"